Add buffers

src/Arch/Core/Buffers/Buffer.cs

@@ -0,0 +1,20 @@
+using CommunityToolkit.HighPerformance;
+
+namespace Arch.Core.Buffers;
+
+public struct Buffer<T>
+{
+    public List<T> Elements;
+
+    public Buffer()
+    {
+        Elements = new List<T>();
+    }
+
+#if NET5_0_OR_GREATER
+    public Span<T> AsSpan()
+    {
+        return Elements.AsSpan();
+    }
+#endif
+}

src/Arch/Core/Buffers/World.BufferElements.cs

@@ -0,0 +1,72 @@
+using System.Diagnostics.Contracts;
+using Arch.Core.Buffers;
+
+namespace Arch.Core;
+
+public partial class World
+{
+    /// <summary>
+    ///     Adds an element to the buffer of an <see cref="Entity"/>.
+    /// </summary>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="value">The buffer instance.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AddToBuffer<T>(Entity entity, in T value = default)
+    {
+        AddOrGetBuffer<T>(entity).Elements.Add(value);
+    }
+
+    /// <summary>
+    ///     Ensures the existence of a value in a buffer on an <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="value">The value to ensure the existence of.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AddOrGetFromBuffer<T>(Entity entity, in T value = default)
+    {
+        ref var elements = ref AddOrGetBuffer<T>(entity).Elements;
+        if (!elements.Contains(value))
+        {
+            elements.Add(value);
+        }
+    }
+
+    /// <summary>
+    ///     Checks if an <see cref="Entity"/>'s buffer has a certain element.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="value">The value to check.</param>
+    /// <returns>True if the buffer has the desired element, otherwise false.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public bool HasInBuffer<T>(Entity entity, in T value)
+    {
+        ref var buffer = ref TryGetRefBuffer<T>(entity, out var exists);
+        if (!exists)
+        {
+            return false;
+        }
+
+        return buffer.Elements.Contains(value);
+    }
+
+    /// <summary>
+    ///     Removes an element from a buffer in a <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="value">The value to remove from the buffer.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void RemoveFromBuffer<T>(Entity entity, in T value)
+    {
+        ref var buffer = ref TryGetRef<Buffer<T>>(entity, out var exists);
+        if (!exists)
+        {
+            return;
+        }
+
+        buffer.Elements.Remove(value);
+    }
+}

src/Arch/Core/Buffers/World.Buffers.cs

@@ -0,0 +1,116 @@
+using System.Diagnostics.Contracts;
+using Arch.Core.Buffers;
+
+namespace Arch.Core;
+
+public partial class World
+{
+    /// <summary>
+    ///     Adds an new buffer to the <see cref="Entity"/> and moves it to the new <see cref="Archetype"/>.
+    /// </summary>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AddBuffer<T>(Entity entity)
+    {
+        Add(entity, new Buffer<T>());
+    }
+
+    /// <summary>
+    ///     Ensures the existence of an buffer on an <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <returns>A reference to the buffer.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ref Buffer<T> AddOrGetBuffer<T>(Entity entity)
+    {
+        return ref AddOrGet(entity, static () => new Buffer<T>());
+    }
+
+    /// <summary>
+    ///     Returns a reference to the buffer of an <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <returns>A reference to the buffer.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public ref Buffer<T> GetBuffer<T>(Entity entity)
+    {
+        return ref Get<Buffer<T>>(entity);
+    }
+
+    /// <summary>
+    ///     Checks if an <see cref="Entity"/> has a certain buffer.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <returns>True if it has the desired buffer, otherwise false.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public bool HasBuffer<T>(Entity entity)
+    {
+        return Has<Buffer<T>>(entity);
+    }
+
+    /// <summary>
+    ///     Removes a buffer from an <see cref="Entity"/> and moves it to a different <see cref="Archetype"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void RemoveBuffer<T>(Entity entity)
+    {
+        Remove<Buffer<T>>(entity);
+    }
+
+    /// <summary>
+    ///     Trys to return a reference to the buffer of an <see cref="Entity"/>.
+    ///     Will copy the buffer.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="buffer">The found buffer.</param>
+    /// <returns>True if it exists, otherwise false.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public bool TryGetBuffer<T>(Entity entity, out Buffer<T> buffer)
+    {
+        return TryGet(entity, out buffer);
+    }
+
+    /// <summary>
+    ///     Tries to return a reference to the buffer of an <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="exists">True if it exists, otherwise false.</param>
+    /// <returns>A reference to the buffer.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public ref Buffer<T> TryGetRefBuffer<T>(Entity entity, out bool exists)
+    {
+        return ref TryGetRef<Buffer<T>>(entity, out exists);
+    }
+
+    /// <summary>
+    ///     Removes a buffer of the given type from an <see cref="Entity"/> if it is empty.
+    /// </summary>
+    /// <typeparam name="T">The buffer's element type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <returns>True if the buffer was empty and removed, false otherwise..</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining), Pure]
+    public bool TrimBuffer<T>(Entity entity)
+    {
+        ref var buffer = ref TryGetRefBuffer<T>(entity, out var exists);
+        if (!exists)
+        {
+            return false;
+        }
+
+        if (buffer.Elements.Count != 0)
+        {
+            return false;
+        }
+
+        RemoveBuffer<T>(entity);
+        return true;
+    }
+}

src/Arch/Core/World.cs

@@ -890,6 +890,26 @@ public ref T AddOrGet<T>(Entity entity, T cmp = default)
         return ref Get<T>(entity);
     }
 
+    /// <summary>
+    ///     Ensures the existence of an component on an <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The component type.</typeparam>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <param name="cmp">The component value used if its being added.</param>
+    /// <returns>A reference to the component.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ref T AddOrGet<T>(Entity entity, Func<T> cmp)
+    {
+        ref var component = ref TryGetRef<T>(entity, out var exists);
+        if (exists)
+        {
+            return ref component;
+        }
+
+        Add(entity, cmp());
+        return ref Get<T>(entity);
+    }
+
     /// <summary>
     ///     Adds an new component to the <see cref="Entity"/> and moves it to the new <see cref="Archetype"/>.
     /// </summary>